Think I was just reading about those the other night. If I am correct they screw into the dropouts from each side and can show the degree of misalignment.

Further on the crank problem I have started dismantling that area and with the chain off the chainrings I can see that there is a wobble of about 1 or 2 mm in the chain ring relative to the bb. This bike does not warrant all this work but I am curious to see if I can correct the problems particularly having spent some time prettying it up with new tires, bearings, bar tape, cables, etc.